Various configurations of electrical transformer are known. The two main types in common use are the core type transformer and the shell type transformer. In the core type transformer, a primary winding and a secondary winding are wound around a magnetic core in the form of a ring. In a shell type transformer, the primary winding and the secondary winding form a common ring which is surrounded by rings of magnetic material distributed about the common ring.
In any transformer it is important to have a high flux within the closed loop of the primary and secondary windings. This may be achieved by increasing the number of primary or secondary windings or both, or by increasing the length of the magnetic circuit. Thus, increasing the cross-sectional area of the core will increase the flux, since the flux is directly proportional to the cross-sectional area of the core. This will increase the performance of the transformer; however, it will also increase the weight of the transformer. Increasing the number of turns in the windings or increasing the area of the core also hinders heat dissipation.
It is generally known that increasing the cross-sectional area of the core also increases eddy currents. For this reason, laminated cores are used in most applications. However, high frequency perturbations in the laminated core cause significant rattling and noise, as is well known, and such laminated cores are difficult and expensive to construct.